This invention relates generally to clinical electronic thermometers for measuring body temperature through the use of a probe. More particularly, it relates to an improved probe construction which is sealed, sanitary and has low thermal mass for quick response of the temperature-responsive element.
Probes for use with associated electrical circuitry for the measurement of body temperature and display of the temperature are well known. The majority of commercial devices are divided into two different types. One is based upon a thermistor element in the end of the probe which changes its resistance with temperature. A basic probe of this type is shown in U.S. Pat. No. 3,025,706--Oppenheim. The other type of probe which has been suggested for an electronic clinical thermometer is a thermocouple type probe, as exemplified in U.S. Pat. No. 4,174,631 issued Nov. 20, 1979 to Hammerslag.
Each type of probe has shortcomings with respect to reaching final body temperature due to the interaction between the probe and the local tissue. When any thermometer device is inserted, it locally cools the tissues, since the thermometer temperature is initially below body temperature. The time required to recover from this effect due to the interaction between the probe and the body is dependent not only on the probe design, but also on the blood circulation and other thermal characteristics of the tissue. The time required for a conventional glass clinical thermometer to reach final tissue temperature is in the neighborhood of 3 to 5 minutes. The primary factor determining this time lag is the thermal mass of the thermometer, which must be brought into substantial correspondence with the local tissue temperature. The local temperature of the tissue must itself also be brought back to where it was before the thermometer was inserted, due to its being cooled down by the thermometer.
Probe preheaters have been employed with thermistors to speed the response by raising the local temperature of the probe in the vicinity of the thermistor, as disclosed in the aforementioned patent to Oppenheim, as well as many other patents exemplified by the following:
______________________________________ U.S. Pat. No. Inventor Issue Date ______________________________________ 3,729,998 Mueller et. al. May 1, 1973 3,485,102 E. N. Glick December 23, 1979 3,893,058 Keith July 1, 1975 3,951,003 Adams October 28, 1975 4,166,451 Salera September 4, 1979 4,133,208 Parlanti January 9, 1979 ______________________________________
Thermistor type probes have been usually favored for clinical thermometers over thermocouple probes, because the electrical circuitry is simpler and because there is no need for a reference temperature or compensation for the cold junction as there is in a thermocouple probe. Normally thermocouples have been used for temperature sensing devices measuring relatively high temperatures over a wide temperature range. This is because the voltage generated is a function of the difference between the hot junction and the cold junction, which favors a large temperature difference. However, with modern electronic techniques and abilities to amplify the low voltages and compensate for changes in cold junction temperature, thermocouple probes are now also practical for clinical temperature measurement.
The aforementioned Hammerslag U.S. Pat. No. 4,174,631 shows a thermocouple probe of low thermal mass achieved by supporting the thermal couple leads in a hollow tube of plastic material and causing the thermocouple junction to bridge the open end of the tube, so that the thin thermocouples support wires and junction are exposed for direct contact with the tissue of a patient. However, since the thermocouple leads are exposed, they may be subject to damage. Also because of the open end of the tube, the probe may become unsanitary due to entry of saliva or foreign matter. Another type of probe with exposed leads is shown in U.S. Pat. No. 4,250,751, issued Feb. 17, 1981 to Holzhacker et. al.
Constructions are known for high temperature type thermocouple probes with sealed ends as exemplified in the following patents:
______________________________________ U.S. Pat. No. Inventor Issue Date ______________________________________ 3,643,509 Surinx February 22, 1972 4,018,624 Rizzolo April 19, 1977 3,880,282 Naumann April 29, 1975 ______________________________________
The problem with the above listed constructions in probes for clinical use is that the large thermal mass on the probe end renders it unsuitable for fast response.
Accordingly, one object of the present invention is to provide an improved probe suitable for clinical electronic temperature measurement.
Another object of the invention is to provide an improved probe having a temperature-responsive element and probe body of very low thermal mass and improved speed of response.
Another object of the invention is to provide an improved construction for an inexpensive probe for a clinical electronic thermometer.